Power supply system provided with photovoltaic generator

ABSTRACT

A power supply system includes a photovoltaic generator, a load to which electric power is supplied from the photovoltaic generator, an electrical system for receiving a portion of the electric power generated by the photovoltaic generator and supplying electric power to the load, and a control unit for controlling the reception and the supply of the electrical power by the electrical system. To ensure that the photovoltaic generator generates electric power at an optimal operational point, the control unit is adapted to not operate when the maximum electric power P max  generated by the photovoltaic generator and an electric power P L  consumed in the load are equal to each other, and to be operated when P max &gt;P L , thereby permitting the electrical system to receive a surplus electric power ΔP 1 , and to be operated when P max &lt;P L , thereby supplying a deficient electric power ΔP 2  from the electrical system to the load.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a power supply system providedwith a photovoltaic generator.

[0003] 2. Description of the Related Art

[0004] Conventional systems are known in which a photovoltaic generatorand a load are connected to each other through a DC/AC inverter (forexample, see Japanese Patent Application Laid-open No.6-133462).

[0005] To conduct the generation of electric power by a photovoltaicgenerator with the best efficiency, it is required that the operationalpoint of the photovoltaic generator is brought into an optimaloperational point.

[0006] However, the optimal operational point varies with the variationin insolation amount, and on the other hand, the current-voltagecharacteristic of the load is substantially constant and the operationalpoint of the photovoltaic generator is determined by the current-voltagecharacteristic of the load. For this reason, it is difficult in theconventionally known system to keep the operational point of thephotovoltaic generator always at the optimal operational point.

SUMMARY OF THE INVENTION

[0007] Accordingly, it is an object of the present invention to providea power supply system of the above-described type, wherein theoperational point of the photovoltaic generator is kept at the optimaloperational point, and a required electric power can be supplied stablyto the load.

[0008] To achieve the above object, according to the present invention,there is provided a power supply system comprising a photovoltaicgenerator, a load to which electric power is supplied from thephotovoltaic generator, an electrical system capable of receiving aportion of the electric power generated by the photovoltaic generatorand supplying the electric power to the load, and a control unit forcontrolling the reception and supply of the electric power by theelectrical system. In order to ensure that the photovoltaic generatorgenerates electric power at an optimal operational point, the controlunit adapted in such a manner so as to not operate when the maximumelectric power P_(max) generated by the photovoltaic generator and anelectric power P_(L) consumed by the load are equal to each other(P_(max)=P_(L)), and to operate when P_(max)>P_(L), thereby permittingthe electrical system to receive surplus electric power ΔP₁(=P_(max)−P_(L)), and to operate when P_(max)<P_(L), thereby supplying adeficient electric power ΔP₂ (=P_(L)−P_(max)) from the electrical systemto the load.

[0009] With the above arrangement, when the maximum electric powerP_(max) generated by the photovoltaic generator and the electric powerP_(L) consumed by the load are equal to each other (P_(max)=P_(L)), theload is operated, and the current-voltage characteristic of the loadcorresponds to the optimal operational point of the photovoltaicgenerator and hence, the operational point of the photovoltaic generatoris at the optimal operational point. In this case, the control unit neednot be operated.

[0010] When P_(max)>P_(L), the load is operated, but the current-voltagecharacteristic of the load does not correspond to the optimaloperational point of the photovoltaic generator and hence, theoperational point of the photovoltaic generator is not at the optimaloperational point. Then, if the surplus electric power ΔP₁ is allowed tobe received in the electrical system, the same state is provided as whenthe power consumed in the load is equal to P_(L)+ΔP₁. Namely, thecurrent-voltage characteristic of the load corresponds to the optimaloperational point of the photovoltaic generator, becauseP_(max)=P_(L)+ΔP₁. Thus, the operational point for the photovoltaicgenerator is at the optimal operational point.

[0011] When P_(max)<P_(L), the load is incapable of being operated.Therefore, if the deficient electric power ΔP₂ is supplied from theelectrical system to the load, the load is operated to provide the samestate as when the electric power consumed in the load is equal toP_(L)−ΔP₂. Namely, the current-voltage characteristic of the loadcorresponds to the optimal operational point of the photovoltaicgenerator, whereby the operational point of the photovoltaic generatoris brought into the optimal operational point. Thus, it is possible toensure that the operational point of the photovoltaic generator is keptat the optimal operational point, and to stably supply a requiredelectric power to the load.

[0012] The above and other objects, features and advantages of theinvention will become apparent from the following description of thepreferred embodiment taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a block diagram of a power supply system provided with aphotovoltaic generator;

[0014]FIG. 2 is a graph for explaining a case where the maximum electricpower P_(max) generated by a first photovoltaic generator and theelectric power P_(L) consumed in the auxiliary equipment are equal toeach other (P_(max)=P_(L));

[0015]FIG. 3 is a graph for explaining a case where the maximum electricpower P_(max) generated by a first photovoltaic generator and theelectric power P_(L) consumed in the auxiliary equipment are in arelation of P_(max)>P_(L); and

[0016]FIG. 4 is a graph for explaining a case where the maximum electricpower P_(max) generated by a first photovoltaic generator and theelectric power P_(L) consumed in the auxiliary equipment are in arelation of P_(max)<P_(L).

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] The present invention will now be described by way of anembodiment of the present invention with reference to the accompanyingdrawings.

[0018] Referring to FIG. 1, a power supply system 1 provided with aphotovoltaic generator includes first and second system sections. Thesecond system section is a water electrolytic system section 2 ₁ as anelectrical system, and includes a low-voltage and high-current typesecond photovoltaic generator 3 as a power generating device, and awater electrolyzer 5 to which electric power is supplied from the secondphotovoltaic generator 3 through a peak power tracker (PPT) 4. The firstsystem section is an auxiliary equipment driving system section 2 ₂ asan auxiliary system of the water electrolyzer 5, and includes ahigh-voltage and low-current type first photovoltaic generator 6 asanother power generating device, a DC/DC converter 7 for converting theelectric power generated by the first photovoltaic generator 6 into aconstant-voltage power, and an auxiliary equipment 8 as aconstant-voltage load to which electric power is supplied from the DC/DCconverter 7. The auxiliary equipment 8 comprises, for example, aninverter, and a water pump driven by the inverter. In this case, thevoltage for operating the auxiliary equipment 8 is higher than that foroperating the water electrolyzer 5.

[0019] The auxiliary equipment driving system section 2 ₂ and waterelectrolytic system section 2 ₁ are connected to each other through acontrol unit 9, so that the control unit 9 enables the waterelectrolyzer 5 to receive a portion of the electric power generated bythe first photovoltaic generator 6, e.g., the electric power from theDC/DC converter and consume it, and also enables a portion of theelectric power generated by the second photovoltaic generator 3 to besupplied to the auxiliary equipment 8.

[0020] The control unit 9 includes a bidirectional step-up/step-downchopper as a bidirectional converter (“BDC”) 10, and a power managementECU (“P/M ECU”) 11. The BDC 10 is connected at its primary side to theauxiliary equipment driving system section 2 ₂ and at its secondary sideto the water electrolytic system section 2 ₁, and exhibits a function ofdropping the voltage in a power flow from the primary side to thesecondary side and a function of raising the voltage in a power flowfrom the secondary side to the primary side. The P/M ECU 11 determinesthe magnitude and polarity of the power flow passing through the BDC 10,based on the electric power input to the DC/DC converter 7.

[0021] In the above-described arrangement, the voltage applied to theauxiliary equipment 8 is converted into V₁ by the DC/DC converter 7, andthe electric power generated by the second photovoltaic generator 3 issupplied through the PPT 4 to the water electrolyzer 5 to conduct theelectrolysis of water.

[0022] When the maximum power P_(max) generated by the firstphotovoltaic generator 6 and the power P_(L) consumed by the auxiliaryequipment 8 are equal to each other (P_(max)=P_(L)), as shown in FIG. 2,the electric power generated by the first photovoltaic generator 6 issupplied via the DC/DC converter 7 to the auxiliary equipment 8, asshown by black arrows a in FIG. 1, and hence, the auxiliary equipment 8is operated. In addition, the current-voltage characteristic coincideswith an optimal operational point for the first photovoltaic generator 6and hence, the operational point of the first photovoltaic generator 6is an optimal operational point. In this case, the BDC 10 of the controlunit 9 need not be operated.

[0023] When P_(max)>P_(L), as shown in FIG. 3, the electric powergenerated by the first photovoltaic generator 6 is supplied via theDC/DC converter 7 to the auxiliary equipment 8, as shown by the blackarrows a in FIG. 1 and hence, the auxiliary equipment 8 is operated.However, the current-voltage characteristic does not coincide with theoptimal operational point for the first photovoltaic generator 6 andhence, the operational point of the first photovoltaic generator 6 isnot the optimal operational point. In such a case, the surplus power ΔP₁is supplied via the BDC 10 controlled by the P/M ECU 11 to the waterelectrolyzer 5 of the water electrolytic system section 2 ₁, as shown bywhite arrows bin FIG. 1, where it is consumed. This provides the samestate as when the power consumed in the load is equal to P_(L)+ΔP₁,namely, the current-voltage characteristic of the load corresponds tothe optimal operational point for the first photovoltaic generator 6,because P_(max)=P_(L)+ΔP₁, whereby the operational point of the firstphotovoltaic generator 6 is the optimal operational point. In the waterelectrolyzer 5, the amount of hydrogen produced is increased inaccordance with the supplying of the surplus power ΔP₁. On the otherhand, if the insolation amount is decreased, the electric powergenerated by the first photovoltaic generator 6 is decreased as shown bya one-dot dashed line in FIG. 3. Then, in accordance with the decreaseof the electric power generated by the first photovoltaic generator 6,the surplus power ΔP₁ is decreased by BDC 10.

[0024] If the DC/DC converter 7 is capable of being operated whenP_(max)<P_(L), as shown in FIG. 1, then the electric power generated bythe first photovoltaic generator 6 is supplied via the DC/DC converter 7to the auxiliary equipment 8, as shown by the black arrows a in FIG. 1,but the electric power generated by the first photovoltaic generator 6is decreased from a range for operating the DC/DC converter 7 and forthis reason, the auxiliary equipment 8 is incapable of being operated.In such a case, the deficient power ΔP₂ is supplied from the secondphotovoltaic generator 3 via the BDC 10 controlled by the P/M ECU 11 tothe auxiliary equipment 8, as shown by arrows c black by half and whiteby half in FIG. 1. Thus, the auxiliary equipment 8 is operated into thesame state as when the power consumed in the auxiliary equipment 8 isP_(L)−ΔP₂. Namely, the current-voltage characteristic of the auxiliaryequipment 8 corresponds to the optimal operational point for the firstphotovoltaic generator 6, because P_(max)=P_(L)−ΔP₂, whereby theoperational point of the first photovoltaic generator 6 is the optimaloperational point. If the insulation amount is increased, the electricpower generated by the first photovoltaic generator 6 is increased asshown by a single-dotted broken line in FIG. 4.

[0025] When the electric power generated by the first photovoltaicgenerator 6 is decreased suddenly, causing the DC/DC converter 7 to beinoperable, the electric power generated by the first photovoltaicgenerator 6 is not supplied to the auxiliary equipment 8.

[0026] Alternatively, the auxiliary equipment 8 can be designed towithstand a variation in voltage of the first photovoltaic generator 6.Therefore, the DC/DC converter 7 can be omitted by combining annualvarying conditions such as the insolation amount, the atmospherictemperature and the like in a place where the system is placed, and thesetting of the number of in-series modules of the first photovoltaicgenerator 6. The electrical system 21 may be an accumulator having abattery.

[0027] Although the embodiments of the present invention have beendescribed in detail, it will be understood that the present invention isnot limited to the above-described embodiments, and variousmodifications in design may be made without departing from the spiritand scope of the invention defined in claims.

What is claimed is:
 1. A power supply system comprising: a first powergenerating device for generating power; a load for receiving the powergenerated from the first power generating device; an electrical systemfor receiving a portion of the power generated by the first powergenerating device and for supplying power to the load; a control systemthat operates to control reception and supply of power by the electricalsystem; and the operation of the control system being a function of themaximum electric power (P_(max)) generated by the first power generatingdevice and the electric power (P_(L)) consumed in the load; such thatwhen the maximum electric power (P_(max)) generated by the first powergenerating device is equal to the electric power (P_(L)) consumed by theload (P_(max)=P_(L)), said control system does not operate; and when themaximum electric power (P_(max)) generated by the first power generatingdevice is greater than the electric power (P_(L)) consumed by the load(P_(max)>P_(L)), said control system operates to permit the electricalsystem to receive a surplus of electric power (ΔP₁)from the first powergenerating device; and when the maximum electric power (P_(max))generated by the first power generating device is less than the electricpower (P_(L)) consumed by the load (P_(max)<P_(L)), said control systemoperates to supply the deficient electric power (ΔP₂) from theelectrical system to the load.
 2. The power supply system according toclaim 1 wherein the control system includes a bidirectional converterhaving a primary side and a secondary side, the bidirectional converterbeing connected at the primary side to the first power generating deviceand at the secondary side to the electrical system; and an ECU fordetermining the magnitude and polarity of the electric power flowthrough the bidirectional converter, based on the electric powergenerated by the first power generating device.
 3. The power supplysystem according to claim 1 or 2 wherein the load is a constant-voltagedevice and is connected to a converter for converting the electric powergenerated by the first power generating device into a constant-voltagepower.
 4. The power supply system according to claim 1 or 2 wherein theelectrical system includes a second power generating device and asurplus power consumption source adapted to receive electric power fromthe second power generating device, and wherein an operating voltage forthe load is higher than that for the surplus power consumption source.5. The power supply system according to claim 3 wherein the electricalsystem includes a second power generating device and a surplus powerconsumption source adapted to receive electric power from the secondpower generating device, and wherein an operating voltage for the loadis higher than that for the surplus power consumption source.
 6. Thepower supply system according to claim 1 or 2 wherein the electricalsystem is an accumulator.
 7. The power supply system according to claim3 wherein the electrical system is an accumulator.
 8. The power supplysystem according to claim 1 or 2 wherein the first power generatingdevice is a first photovoltaic generator.
 9. The power supply systemaccording to claim 3 wherein the first power generating device is afirst photovoltaic generator.
 10. The power supply system according toclaim 4 wherein the first power generating device is a firstphotovoltaic generator.
 11. The power supply system according to claim 5wherein the first power generating device is a first photovoltaicgenerator.
 12. The power supply system according to claim 6 wherein thefirst power generating device is a first photovoltaic generator.
 13. Thepower supply system according to claim 7 wherein the first powergenerating device is a first photovoltaic generator.
 14. The powersupply system according to claim 4 wherein the first power generatingdevice is a first photovoltaic generator and the second power generatingdevice is a second photovoltaic generator.
 15. The power supply systemaccording to claim 5 wherein the first power generating device is afirst photovoltaic generator and the second power generating device is asecond photovoltaic generator.
 16. The power supply system according toclaim 4 wherein the surplus power consumption source is a waterelectrolyzer.
 17. The power supply system according to claim 5 whereinthe surplus power consumption source is a water electrolyzer.
 18. Thepower supply system according to claim 10 wherein the surplus powerconsumption source is a water electrolyzer.
 19. The power supply systemaccording to claim 11 wherein the surplus power consumption source is awater electrolyzer.
 20. The power supply system according to claim 14wherein the surplus power consumption source is a water electrolyzer.21. The power supply system according to claim 15 wherein the surpluspower consumption source is a water electrolyzer.